One vertex per element, one color per generator, with an edge from x to x·s.
(2,5)(6,8)(11,16)(12,15)(25,26)(27,28)(29,34)(30,31)(32,33)(35,36)(37,38)(39,40) involution — undirected(9,10,14,13)(11,15,16,12)(18,22)(23,24)(26,31)(27,33)(29,37)(36,39)(9,11,14,16)(10,15,13,12)(17,18)(19,23)(20,24)(21,22)(25,27)(26,32)(28,31)(29,35)(30,33)(34,39)(36,38)(37,40)(1,2)(3,6)(4,5)(7,8)(9,12)(10,11)(13,16)(14,15)(17,19,21,20)(18,23,22,24)(25,28,30,32)(26,33,31,27)(29,36,37,39)(34,40,38,35)(1,3,4,7)(2,6,5,8)(9,13,14,10)(11,12,16,15)(17,20,21,19)(18,24,22,23)(25,29,30,37)(26,34,31,38)(27,35,33,40)(28,36,32,39)A Cayley diagram is a choice, not a fact about the group. Another drawing of this group — in a book, or on a different generating set — may look nothing like this one.